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Volume: 1995/1


Title: The influence of band saw strain force on idling power
Author: Vlado Goglia, Ružica Beljo

Strain force is a very important parameter of the general efficiency of the band saw. In order to point out the importance of strain force the paper presents research results of its influence on the machine\'s idling power. As independent variables two parameters have been chosen: strainforce and cutting speed. References mention a wide range (from 30 to 120 MPa) of optimum strain force values. The choice of the optimum strain force value will thus provide for the higher efficiency of the band saw. For the purpose of the research described in this paper, strain force was measured by an approximative method of measurement. The band saw blade was loaded by a horizontal force of a controlled value. At the same time the lateral inclination of the band saw blade was measured as well. The power of the machine\'s own resistances was measured at various strain forces. At each level of the strain force cutting speed has been varied by changing the rotation frequency of the electromotor. The change was performed with a frequency transformer. Measurement results are analysed and graphically represented. The influence of electromotor rotation frequency on the machine\'s idling power is linear and expected, but fhe influence of strain force cannot be called linear, which is an unexpected result.

Title: Some physical and mechanical properties of the Bednja abonos
Author: Slavko Govorčin, Tomislav Sinković

Oakwood buried in the ground, or abonos, is subfossil wood which has been exposed for a very long time to the process of humidification under the influence of running fresh water. It is black in colour due to a chemical reaction between the tanstuff in the wood and the contents of iron in the water. Besides this change in colour, there are some other significant alterations of the physical und mechanical properties of oak wood. Although some of its properties have changed for the worse compared to the recent oakwood, there is a great demand for the oak abonos, especialy when used as veneer, for interior furnishing and manufacture of precious furniture, parts of musical instruments und decorative woodwork.

Title: Some structural characteristics of ashwood (Fraxinus angustifolia, Vahl.) from the Lipovljani region in Croatia
Author: Božidar Petrić, Jelena Trajković, Radovan Despot

Among various problems concerning rational processing of thin logs, this work discusses the structure of juvenile and adult ashwood. Variations in fiber lengths und diameters, thicknesses of their membranes, diameters of late wood and early wood vessels, and volume percentage of vessel members, width and height of rays und ray volume percentage have all been researched. Necessary measurements in annual rings (age 5, 10, 20, 40, 70 and 100) have been made. It has been established that juvenile ashwood spreads from the pith up to approximately 40th annual ring.

Title: Drying of 32 mm oak-wood boards - comparison of the experimental and production kiln-dryng schedules
Author: Stjepan Pervan

Drying properties of domestic wood species, especially oakwood, have prompted an analysis of 32 mm thick oakwood kiln-drying schedule. The schedule was applied in production conditions and was compared with the knowledge achieved through research and praxis in the world. Today drying schedules are just partially customized to different species und dimensions of dried wood, so that the drying process has to be conducted with respect to characteristics of wood in an area and drying-kiln conditions in question. The research was conducted in conventional drying kiln using a stack of 32 mm oakwood boards. At the beginning of the process the dry-bulb temperature (30°C) of the tested schedule was too low from the point of view of energy consumption, and the difference between the dry and the wet-bulb temperature was appropriate concerning the possibility of drying defect development. During later drying phases, approximately at the fiber saturation point, the dry-bulb temperature of 48°C and the difference between the dry and the wet-bulb temperuture of 5°C were low when compared to the values listed in references. Drying from 30% moisture content to the final moisture content took place at a lower dry-bulb temperature, except during the period from 30 % to 10% moisture content, but it became too high below 10 % moisture content. The kiln-schedule analysis suggests that the experimental kiln- schedules have to be fitted to real conditions before they are applied, and that even then careful operation and correction is needed throughout the drying process.

Title: Accelerated weathering of wood surfaces - The QUV accelerated weathering tester
Author: Hrvoje Turkulin, Vlatka Jirouš-Rajković

Wood durability is affected by outdoor climatic conditions, mainly by action of light and moisture. High maintenance costs determine the need for investigation of photodegradation process and means of its prevention. The QUV is an accelerated weathering apparatus which serves to predict the relative durability of materials exposed to outdoor environment. Rain and dew are simulated by a condensation system and the damaging effects of sunlight are simulated by fluorescent UV (ultraviolet) lamps. Materials are tested by exposure to alternating cycles of light and moisture, at controlled, elevated temperatures. In a few days or weeks, the QUV can reproduce the damage that occurs over months or years out of doors.





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